Telephone system



L.. J. BC'WNE TELEPHONE SYSTEM Jan. 13, 1925. 1,522,862

Filed Sept. 7. 1922 3 Sheets-Sheet l o Q V- f-JIW n* Q l N JIMIMM Langford J Bow/7@ by AHV.

Jan, 13, 1925.'

L. J. BOWNE TELEPHONE SYSTEM Filed Sept. 7, 1922 3 Sheets-Sheet 2 bww lnvenor: Langford J 50W/7e mmv..

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L. J. BOWNE TELEPHONE SYSTEM m .\N/ w um@ u@ a Qn H mw w H v @W l 1MM] Sm! 2` @uw /NN 7 i W @uw Qn mmm( n A i l u mmh. mn@ m. @Y @9Min IRQ Qn lnvenlor: Langford J. Bowne Patented Jan. 13, 1925.

LANGFORD J. B OWN'EV, O'F 11T.OVV'JLILLDL NEFvJ YORK, ASSIGNOR TO VESfTER-N ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORKy N. Y., A CORPORATION OF NEW YORK.

TELEPHONE sYsTnM.

Application filed September 7, 1922. Serial No. 586,615.

To all 1.0710722., t 72.2.03/ concern:

Bc it known that l, Laxoronn J. Bownn, a citizen of the United States, residing at Howard Beach, in the count-y of Queens, State ot' New York, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems and more particularly to switching systems wherein toll switching trunks are employed to establish telephone connections between distant subscribers.

It is the usual practice in establishing connections between a toll line and a subscribers station to employ a cord circuitat a toll operator's position and a toll switching trunk extending from the operators position to a B operators position at an otce in which the calling or called subscribers station is located. Complete supervision of the connection in such systems is accorded the toll operator by the provision of supervisory signals in the cord circuit which indicates to the operator when either subscriber answers, hangs up the receiver or flashes.

The supervisory conditions mentioned above introduce marginal conditions which necessitate an exactness ot relay design.

ln one system oiI the character mentioned, it has been customary practice to employ the sleeve or third wire ot the lineand cord circuits for selecting the type of supervision to be given by the cord circuit, and wherein such a condition prevails, it is the usual practice to employ three relays in the sleeve conductor vto meet the necessary marginal conditions previously mentioned.

Objects ot this invention are therefore to obviate the exactness of relay design required and to remove one of the above mentioned marginal conditions.

It is a .further object or" this invention to employ the ring conductors of the line and cord circuits used in such systems for selecting the type of supervision to be given by the cord circuit.

Another object ot this invention is to maintain the supervisory selecting means disassociated from the line during the period ot conversation.

A. further object otthis invention is to prevent the release of a relay due to a shunt t ircuit temporarily established therefor during the existence ot a locking circuit tor such relay.

In accordance with features of this invention, the system hereinafter to be described provides a cord circuit and a call circuit toll line wherein the ring conductors are employed lltor selecting the proper relays in the cord circuit for supervisory purposes, and thereafter the supervisory selecting apparatus is removed from the ring conductor.

Aanother 'feature ot this invention resides in the provision ot locking circuits for two relays connected to the ring conductor, said circuits including resistance elements which are also included in temporarily established shunt circuits for the relays to prevent their release.

A clear understanding ot the invention will be had from the following detailed description and by reference to the accompanying drawings in which F ig. l shows a subscriberls station and a toll switching` trunk; Fig. Q shows a cord circuit embodying teatures of this invention, and the terminals of call circuit toll line and of a ring-down toll line to which circuits the cord circuit is particularly applicable, and Fig. 3 shows the remaining portion ot the call circuit toll line and a subscribers station.

Assuming that the subscribers on lines L and i3 are located at stations separated by a considerable distance and that telephonie connection is desired between these subscribers, the subscriber at being the calling subscriber and the subscriber at l the called subscriber, the procedure is as' follows: y

T he subscriber a' A initiates a call in the usual manner and causes the operation ot line signals at a central office. Upon noting the illumination ot a line lamp such as 11.2, the originating operator inserts the plug ot' an idle cord (not shown), associated with her position into the answerino` jack associated with the calling subscribers line and operates her talking key to connect her telephone set with the calling subscriber in order to ascertain the natureof the call. Upon learning that a subscriber B is desired, the operator dismisses the calling subscriber and proceeds to establish the ronnection. T he method and means employed. whereby the originating operator signals other operators who may be called to complete the connection, and the method of assigning the circuits to be employed in completing the connections are well known in the art and need not be described herein.

After the assignment of a toll switching trunk to be employed in establishing the desired connection, the local inward operator inserts the plug ot this toll switching trunk into the jack 101 of the line of the calling subscriber A while an outward operator inserts the plug 201, associated with one end ot the cord circuit, into the jack 202, which is associated with the toll switching trunk assigned by the local inward operator.

Upon insertion of the plug 100 into the jack 101 ot the calling subscribers line, a series circuit is established for relays 102 and 103, which may be traced from grounded battery, through the winding of relay 103, over the sleeve contacts of plug 100 and jack 101 and thence to ground through the winding ot relay 102. The operation of relay 102 disconnects signaling battery from the subscribers line A and releases relay 104C thereby extinguishing line lamp 112. The operation of relay 103 disconnects the operators telephone set from the tip of the cord circuit and makes the tip conductor continuous. Relay 103 also prepares a circuit for lamp 108 which may be traced from grounded battery, through the filament of lamp 108, the lower armature and front contact of relay 103, conductor 113 to the back contact of relay 109, which relay has been operated upon the insertion of plug 201 into the jack 202. Then plug 201 was inserted in jack 202 relay 203 operated over a circuit extending from grounded battery, through the winding of relay 203, and thence to ground over the sleeve contacts of plug 201 and jack 202. Relay 203, in energizing, establishes an obvious circuit for relay 204. Relay 2011, upon energizing, disconnects the outward operators telephone set busy test circuit from the cord circuit and makes the tip conductor thereof continuous. Relay 204, thereby establishes a circuit which may be traced from grounded battery, through the right-hand winding of relay 109, conductor 114, normal contacts of relay 105, conductors 115 and 116, through the lower righthand winding of repeating coil 107, over the ring conductor 117, the ring contacts of jack 202 and plug 201, the lower normal contact of ringing key 217, conductor 220, right-hand winding of retardation coil 205, through the winding of relay 206, left-hand winding oi retardation coil 205, conductor 221. upper normal Contact ot ringing key 217, through the armature and front contact of relay 2011, over the tip contacts o1 plug 201 and jack 202, tip conductor 118, the upper right-hand winding of repeating coil 107, conductor 119, the lett-hand armature and back contact of relay 105, conduct'or 120, and thence t'o' ground through the left-hand WindingV of relay 109. Relays 109 and 206 energize in this circuit. Relay 109, in operating, prevents at its armature and back contact, the

illumination of lamp 108 over the circuit hereinbefore traced, in part. Relay 206, 1n operating, establishes an obvious circuit for lamp 2.07. The outward operator then connects her telephone set to the telephone set of the operator at a distant toll oirlce, at which oiiice the line of the called subscriber terminates over a call circuit, which is not shown but is well known to those skilled in the art, and informs this operator that the party on line B is desired.

This distant operator then assigns a call circuit toll line to the outward operator and inserts the plug 300 of the call circuit toll line into the jack 301 which is associated with the called subscribers line and the outward operator inserts plug 208 into jack 209 of the assigned toll line circuit. The insertion of the plug 300 into the jack 301 estab lishes a series circuit tor relays 302 and 303 .if

which may be traced from grounded battery, through the winding of relay 302, over the sleeve contacts of plug 300 and jack 301, and thence to ground through the winding of relay 303. VRelay 303 operates and disconnects the line relay 304C from the subscribers line, thereby preventing the operation et' line lamp 350. Relay 302 prepares a circuit' for relay 318, which"circuit is open at the. armature and front contact of relay 315..

`When the outward operator inserts plug 208 of her cord circuit into the jack 209 of the call circuit toll line, a circuit is estab?. lished eXtending from grounded battery, through the winding of relay 212, the lefthand armature and back contact of relay 213, over the ring contacts of plug 208 and jack 209, over the ring conductor 330 of the call circuit toll line, the normal contacts of relay 306, conductor 331, and thence to. ground through the winding of relay 307. It is to be noted that the sleeve circuit through relays 210, 211 and 306, up to this time, has been open at the contact of relay 307. Relay 212, in operating, transfers the supervisory lamp 215 from the ring-down supervisory circuit to the third wire supervisory circuit which is one of the features of this invention. Relay 307, in operating, establishes a circuit extending from grounded battery, through the windings ot relays 210 and 211, over the sleeve contacts of plug 208 and jack 209, the left-hand armature and front contact of relay 307, the winding of relay 306 to ground. Relay 210, being marginal, does not operate in the circuit ljust traced. The circuit through the resist ance element 309 which .is normally bridged across the winding of relay 306 is open at the Contact of relay 320 which relay operates Atromthe middle contact `ofrelay307 l s n, cuits traced therefor.

*,energ-ifzation of relay 307:1. circuit is les- Relay 211 operates .in this circuitl andestablishes .an vobvious circuit for relay, 213 and also establishes a locking circuitfor relay 212, Which may be traced from grounded battery through the vvintlingof relay 212, through the right-hand armature and front contact of relay 212, .throughthe resistance ele1nent214, and thence to ground through the. armaturelandfrontcontact oit relay 211.

The resistance element 214is included ,in the locking circuitjtor relay212 in orderto prevent the short circuiting and therefore, the deenergizvation of relay 307. It Will be noted that immediatelyupon the operation oi relay 211, a momentary shunt-aboutielay 307 may Ybe-tracedA from ground, through the Winding of relay 307, conductor 331, normally closed contacts of relay 306, conductor 330, ring contacts of jack 203 and plug 208, left hand armature andb aclcoir tact ot relay 213, right-hand armatureand frontl contact of relay 212, `resistance ele ment 214 to ground at the armature and front contact .of relay 21.1. Owing. Ato the inclusion of resist-,ance element-211km the,l circuit just traced, relay 307 which would',y otherwise have been released by `such shunt,y

maintainedenergized. Relay213, ,in (gperating, disconnects the Winding., ot' relay 2121110111 the ring conductor oftheitoll cord. 4

lt is to be notedironrthe preceding Adescription that the selection of supervisory relay in thegcord` circuit is accomplished over the ring conductors of thecord--and line. circuits and-afterthe selection has-been made lthe selecting circuit is removed ,from the ringronductor. Relay 306, operating in the circuit previously traced, `remoyesthe Winding of relayy 307 from the ring conduc? tor of the call circuit toll lineand establishes a locking circuit for this relay Which may be traced from grounded battery, through the resistance element 303, through the armature and frontcontact of relay306,` conductor 331 and thence to ground through the winding of relay 307. Y 'Y lVhen relay 306 is operating there is a momentary circuit existing which may be. traced from the grounded positive pole of battery, through resistance elementy 308, armature and make-and-break contacts yof relay 306, conductor 330ring contacts of jack 209 vand plug208, left-handarmature and back contact of relay213, Windingpf relay 212, through the positive `pole vo:t=bat\ tery to ground. The two batteries are then in opposition, but relay 212 is maintained operated oWingto. the presenceof theresistance element 308 until the normally,l closed contacts of relay 306 ,are opened...

Relays 211, 213 and 306 operate'in the order named. to effect the proper. functioning ot' relays 212 and 307, the latter re- `160,and thenceto ground, through the p ture.andfrontcontact of relay 315. Relay .,318operates inlthis circuit` and impresses laysl krernainiing `locked over I the. locking cir- As a result of the tablished from ground, ,frontv contact .and

innerright-hand armature of relayl307, con-l. ductortl, armatureand contact of, relay` 313, conductor Winding ot'relay 320 to, battery-.and ground., Belayin operatT ing-,opens the circuitof yrelay.324,1 to pre-` ventthe-operation of .relay 432,1at thisl time, Consequently the ground on conductor 341 is now also Aextended vthrough thev armature and, back. contact of relayk 322, the back contact and armature of relay., 324, Winding of relay 321` to `battery. andgrotuid causingfthe energization ofrelay. Re'lay30`7, at its .outerrightT handarmaturei .and front Contact, .establishes a circuit extending from grounded,

battery, through `theright-hand winding. of

retardationcoil`310, the outer right-hand armaturey and baclrqconltactot relayI `311, the, lovver right-hand windingotl repeating coil.3,12`, conductor 313 of the` line, thelower vleft-hand Windingmof repeating lcoil 3141,

conductor 351, throughthe Winding otrewinding,orepeating.coil 314, tip conductor 31.7,. of, the line, upperyright-,hand winding ofrepeatingco-il 312,'. conductor .337, the

outer, right-hand., armature .and .front corr. tact .of relayA 307, conductor333, V,the ,inner right-hand armature and `back Contact of relay.,.311, andthence togroundl through the left-hand Winding of retardation coil, 310.

,pletes the .circuit previously prepared for relay 318i-,by the Voperation yotrelay 302, which may* betraced from ,grounded battery '.throzughthe Winding ofzrlelay; 318, conductor 339, rightfhand yarmature and front contact vof relayf302, the lett-hand armature andbaclccontactof relay 305, conductor ringingcurrent from the source 310over the call circuit tollvline. conductors 317 and.

313andthe windings of repeating coil 314,

Ywhereupon relay 319 is energized. Relay 313,'inoperating, opens thefcircuit through `the Winding of relay., 320, which releases, thereby closing the shunt. around the Windingof relayv v306 including. the resistance ielement 309, thus reducing the resistance of jthe sleeve circuit sufficiently to permit the operationbf marginal relay 210. Relay andtheuce to ground through the middlev left-hand armature and front contact of relay 212.

The illumination of the lamp 215 informs the outward operator that the line of the subscriber at station B has been connected to the call circuit toll line and she thereupon proceeds to ring the called station B by operating the ringing key 216, which impresses ringing current from the source 235 over the tip and ring contacts of plug 208 and jack 209 through the contacts of relay 321., and thence through the winding of relay 322. It should be noted that during the energiza tion of relay 319 and the consequent deenergization of relay 320, that relay 324 be comes operated through the left hand armature and back contact of relay 320 so that the energizing circuit of relay 321 previously traced is opened thereby connecting the trunk conductors to the relay 322 so that this relay may now be operated. Relay 322, in operating, opens the circuit for relay 321 to prevent this relay from operating at this time, and establishes a circuit which may be traced from grounded battery, through the winding of relay 311, conductor 344, .the armature and front contact of re-v lay 322, conductor 341, and thence to ground through the inner right-hand armature and front contact of relay 307. Relay 311., in operating, reverses the polarity of the battery through the retardation coil 310, over the tip and ring conductors 317 and 313 of the call circuit toll line in order to operate the polarized relay 316. This reversal of polarity does not affect the operation of relay 315. Relay 316, in operating, establishes a circuit for relay 323, which may be traced *from grounded battery, through the winding of relay 323, conductor 345, and thence to ground through the armature and Jfront contact of relay 316. Relay 323 energizes and impresses ringing current from the source 340 over the armatures and front contacts of relay 323, over the tip and ring contacts of plug 300 and jack 301, and thence over the line to the subscribers station B in order to ring the called subscribers bell. "When the operator releases ringing key 216, relay 322 releases and opens the circuit for relay 311. Relay 311, in deenergizing, again reyerses the polarity of the battery on the tip and ring conductors 317 and 313 in order to release the polarized relay 316 which, in turn, interrupts the energizing circuit for relay 323, thereby removing the ringing current source 340 from the called subscribers station. l

Vhen the called subscriber removes the receiver from the hook an energizing circuit is established for relay 305. The circuit for relay 305 may be traced from grounded battery, through the winding of relay 305, conductor 354, over the ring contacts of plug 300 and jack 301, through the telephone apparatus at station B, over thev tip contacts of jack 301 and plug 300, comductor 350, and thence to grotuid through the resistance element 367. Relay 305 opens the circuit for relay 318 which in turn removes the ringing current from the line and releases relay 319. The release of relay 319 establishes an operating circuit for relay 320 extending from grounded battery through the` winding of relay 320, conductor 352, armature and back contact of relay 319, conductor 341, inner right-hand armature and front Contact of relay 307 to ground: Relay 320 thereupon energizes and opens the shunt around relay 306, thereby increasing the resistance of the vsleeve circuit to such an extent as to effect the release of relay 210 which at its arn1ature and front contact opens the circuit for supervisory lamp 215. Relay 320 also opens the circuit of relay 324 which releases and closes the circuit for relay 321 which thereupon energizes and makesthe talking conductors continuous.

A connection now exists between the called subscribers line and the outward operator which may be traced over the tip and ring vcontacts of jack 301 associated with thecalled subscribers line, the tip and ring contacts of plug 300, the upper and lower armatures of relays 323 and 318, the windings of repeating coil 314, over the tip and ring line conductors 317 and 313, the windings of repeating coil 312, the armatures and front contacts of relay 321, the tip and ring contacts of jack 209, the tip and ring contacts of plug 208, through the normal contacts of ringing key 216 and the normal contacts of talking key 218,V conductors 240 and 241, and thence to lthe operators telephone set through the contacts of key 234.

The calling subscriber is then rung by, the operation of ringing key 217, which impresses ringing current from the source 242, over the tip and ring contacts of plug 201 and jack 202, the tip 'and ring conductors 118, and 117 of the toll switching trunk through the right-hand windings of repeating coil 107, and thence through the conductors 122 and 123, through the winding of relay 124. Relay 124 thereupon energizes and establishes a circuit extending from grounded battery throughthe righthandv winding of relay 105, conductor127, through the winding of relay 125, conductor 126, and thence to ground through the armature and front contact of relay 124. Relay 125 thereupon energizes and connects ringing current from the ringing current source 128 to the tip and ring conductors of the cord, tip and ring contacts of plug and jack 101 and thence over the subscribers line loop to operate the bell at through the winding of'relay 111, the lower Maase?,

moves the receiver froml the switchhoo-k` and proceeds to converse with'the called' for subscriber. y

The supervisory lamp 207 which indicates the response of the calling subscriber, is eX- tinguished when this subscriber lremoves the 4receiver from the switchhook to cause relay 111 tooperate. The circuit for relay 111 may be' traced trom grounded battery left-hand winding of repeating coil 107, throughthef armature Aand normal contact of relay`125`, the ring contacts of plug 100 an'd`jack 101 through the telephone apparatus'at subscribers 'station A over the tip contacts ofjack 101 and plug 100,v the'up- "per armature and front contact of relay ingtrunk, jack 202,'*plug 201, retardation coil 205 and the ywindings 'of relay v206. Re-

lay-206 thereuponis deenergized and opens the circuit'for supervisory lamp 207.

The toll operator mayl converse vwith the called subscriberiby the operation 'of splittingkey` 219, without the calling subscriber hearing the conversation, and'in a like manner by operating the splitting key 218, she

vmay converse with the calling subscriber without the lcalled subscriber'hearlng the conversation.

Upon the termination of the conversation,

the called subscriber in replacing the receiver upon'the switch-hook releases relay 305. f The closure of the left-handarmature and back contact of relay305 completes a Acircuit for relay 318 corresponding to that established when yplugs 208 and 300' wereA inserted intojacks 209`and 301 respectively. Ringing current from source 340, thereupon operates relay 319 which, in turn, releases relay 320 to re-establish the shunt circuit aroui'idrelay 306 permitting marginal relay 210 to` operate and cause the illumination of lamp 215 inthe manner previously de-` scribed.` However, the illuminationot lamp 215 at this time servesas a disconnect signal.

`lelay` 320 in releasingalso operates relay 324 and thereby releases relay 321 to render the talking conductors of the toll line discontinuous and to'v reconnectlrelay `322`to`one portion thereof. lhen thereceiver is replaced upon the switchhook at the calling station, relay 111 releases to release relay 105v thus reconnectingbattery and ground throughthe windings of relay 109 toconductors 117 and 118 Vfor operating vrelay 206 to cause the illumination of lamp 207 to serve as a disconnect signal from station A.

The outward operator, noting the disconnect Asignals actuates listening key 234 and upon ascertaining that the conversation has ceased, removes plugs 201 and 208 from their respective' jacks. rlihe removal of plug 201 from jack 202 opens the circuit ot' and releases relays 203 and 109 to close an obvious circuit for lamp 108 and to open the circuit oit lamp 207. The illumination of lamp 108 serves as a disconnect signal to the toll switching trunk operator who thereupon removes plug 100 rom pack 101, restoring to normal allapparatus ofthe line circuit includingstation A andthe toll switching trunk.

l The removal ot' plug 208 from jack 209 releases all operated relays of the cord' circuit and releases relays 306 and-307 removing battery and ground from conductors 313 and -317 to cause the release of relay 315. Lamp-470 is then illuminated as a disconnect signal over a circuit traceable from grounded battery through the lilament of Vlamp 470, right-hand armature and back contact of relay 305, conductors 471 and 473, the Vleft-hand armature and front contact of relay 302,'conductor 474 and the armature and Vback contact of relay 315 to ground. The outward operator noting this signal removes plug 300 from jack 301, thus restoring to normal all remaining -operated apparatus.

The following description is directed to the estab-lishment of a connection between vdistant subscribers wherein a ring-down toll line is substituted-for the call circuit toll line employed in the preceding description. In order to show: the functions of rthe toll cord circuit with a ring-clown toll line, it is only necessary to describe how supervision isobt'ained and how the supervisory signal in the cord circuit is actuated on a ring incoming from a ring-down toll line as the other operations are common to ring-down circuits and are well known in the art.

l/Vhen the called subscriber is to be reached over a ring-downtoll line, the outward operator inserts plug`208 into jack 230 and operates ringing liey- 216 which impresses ringing current from the source 235 to cause the signal at the distant station to operate'. vWhen" plug 208 is inserted in jack 230, a.

circuit is established extending from grounded battery through -the windings 0i' relays 210 and 211, sleeve contacts ofplug'208 and jack'230 to ground. Theresistance of this circuit is sof low asto permitV the operation of relays 210'and 211. Relay 212 does not cuit toll line. Relay 211, in operating, establishes an energizing circuit for relay 213 which, in turn, at its left-hand armature and back contact, disconnects the winding of relay 212 from the ring conductor I0f the cord circuit and at its right-hand armature and front contact connects the tip conductor on the cord circuit to the operator-s telephone set. Relay 210 establishes an energizing circuit for relay 231 extending from grounded battery, armature and front con tact of relay 210, innermost left-hand armature and back contact of relay 212, conductor 246, winding of relay 231, and thence to ground through the armature and back contact of relay 232. Relay 231, in operating, prevents the illumination of the supervisory lamp 215 and the operation of relay 233 at this time.

When the operator at the distant ofiice desires to signal the' calling operator, she impresses ringing current upon the line by the operation of a ringing key similar Vto thatY shown at 216, whereupon relay 232, which is normally bridged across tip and ring conductors of the cord circuit, is energized and at its armature and back contactopens the circuit kof relay 231. Relay 231, in releasing, establishes a circuit foil supervisory lamp 215 extending from grounded battery, the armature and front contact of relay 210, the iilament of lamp 215, the middle armature and back contact of relay 212, conductor 245, armature and back contact of relay 231, conductor 246, and thence to ground through the lowest normal contact of key 234. Relay 233 being bridged around lamp 215 operates and locks up, keeping the lamp lighted until the operator actuates key 234. Upon noting this signal, the operator operates key 234 to connect her telephone circuit to the cord .circuit in a f manner similar to that described in the iirst case.

From the foregoing description., it is obvious that the toll cord circuit functions withthe ordinary type of ring-down toll line to select the proper relays for supervisory purposes as well as with the call circuit toll line shown in Fig. 3 and hereinbefore described.

What is claimed is:

1. In a telephone system, a line circuit, a cord circuit for connection therewith, each of said circuits having a plurality of conducto-rs, a signaling device normally associated with one conductor of said cord circuit, means controlled over said conductor and the corresponding conductor of said line circuit and responsive to the intercon-A nection of said circuits for disassociating said signaling device from said conductor of said cord circuit and associating it with another conductor of said cord circuit, and' means for thereafter controlling said signal-f ing device over other conductors of said line and cord circuits. Y

2. In a telephone system, a line circuit, a link circuit for connection with said line, said circuits having talking and signaling conductors, a signaling device in one of said circuits, and means associated with one of the talking conductors of said circuits for transferring the device to the control of a signaling conductor of said circuits.

3. In a telephone system, a line circuit, a link circuit for connection therewith, said circuits having tip, ring, and sleeve conductors, a signaling device in one of said circuits, and a plurality of relays associated with the ring conductors of said circuits for preparing said signaling device for operation and thereafter transferring the control of said signaling device to the sleeve conductors of said circuits. p,

4. In a telephone system, a line circuit, a cord circuit for establishing a connection therewith, said circuits having tip, ring, and sleeve conductors, a signaling device associated with the ring conductor of .said cord circuit, relays associated with the ring conductors of said circuits and responsive to the connection of said cord circuit with said line circuit for disassociating said signaling device from said ring conductor, and relays in said cord circuit for establishing locking` circuits for said first mentioned relays for maintaining said relays disassociated from said conductor during the continuance of the connection of said cord circuit with said line circuit.

5. In a switching system, two relays, an operating circuit therefor, switching means controlled by a separate circuit to close locking circuits for said relaysv and to open said ope-rating circuit, shunt circuits for said relays closed by said switching means after the closure of said locking circuits, and means in said shunt circuits for preventing the release of said relays due to said shunt.

Y 6.- In a switching system, a relay adapted to operate or hold upon the flow therethrough of currents of predetermined values, a circuit for operating said relay, switching means to close a locking circuit for said relay and thereafter open said operating circuit, and a shunt circuit established for said relay while said circuits are closed to reduce the amount of current flowing' through the winding of said relay to said predeterminedholding value thereby preventing the release of said relay.

7. In a switching system, a relay adapted to operate and to release upon predetermined values of current flow, a circuit for operating said relay, means to close a locks ing circuit therefor and thereafter to open said operating circuit, a shunt circuit for said relay established by said means while said circuits are closed to decrease the current through the relay to a value in eXe'ess of said predetermined releasing Value.

8. In a. switching system, two relays, an operating circuit therefor, a. second circuit closed by the operation of one of said relays, a plurality of relays included in said seeond circuit to Close independent looking and shunt circuits for each of said first inentioned relays and to thereafter' open said operating circuit, and means included in said shunt circuit to prevent the release of said first mentioned relays.

In Witness whereof, I hereunto subscribe my name this 1st day of September, A. D.,

LANGFORD J. BOVNE. 

